The crew was able to inspect and make repairs on the vessel while in orbit.
CAPE CANAVERAL, Fla. -- America's space agency found comfort Sunday in official routines ahead of Discovery's return, while the rest of the world looked skyward and inhaled amid preparations to welcome home the first space shuttle to fly since the 2003 Columbia tragedy.
It has been a mission disconcertingly similar to others before it. Columbia disintegrated on re-entry when superheated gases found a chink that foam debris left after hitting heat-resistant tiles.
Like Columbia, a large chunk of foam insulation also tore away from Discovery's main refueling tank during launch. Future shuttle launches have been canceled until the problem can be fixed.
But unlike Columbia, the foam did not appear to strike the orbiter. And unlike any previous flight, astronauts aboard Discovery have had the unprecedented ability to probe their own craft for weaknesses and do self-repairs in orbit.
They made one repair: Astronaut Stephen Robinson pulled two strips of protruding tile filler from Discovery's underside. They rejected another: The National Aeronautics and Space Administration judged a torn thermal blanket under mission commander Eileen Collins' cockpit window -- likely ripped by launch debris -- was good enough for re-entry.
With weather forecasts promising manageable patchy clouds for an overnight landing, the outcome of those decisions was to be put to an ultimate life-or-death test above Central America early today.
Return to Earth
In an irreversible process beginning around 2 a.m. today, the shuttle was set to dive into the atmosphere at 17,500 mph, turning the atmosphere ahead of it into 3,000-degree plasma during its drop toward Florida's Atlantic coast.
NASA confidently has predicted success. But as the day wore on Sunday, fingers were crossing.
In orbit, Discovery crew members spent much of the day stowing equipment and readying their orange launch and entry suits. Collins, Robinson and pilot James Kelly practiced landing procedures on a laptop computer.
"As you get closer and closer to the ground, things start happening faster and faster, and the last two minutes of the flight, there are a lot of calls going on," Kelly said.